In digital communications systems, data are transmitted serially. It is therefore necessary to convert the data to parallel format at the receiver. To facilitate this conversion, sync words are inserted in the data stream to define data words, frames and subframes or paragraphs. These sync words are sometimes called unique words because their patterns of binary 1's and 0's are highly self-correlative and therefore readily recognizable. The process of recognizing the sync words and converting the serial data stream to parallel format is known as frame synchronization.
Frame synchronizers have in the past comprised a serial-to-parallel converter, sync word comparators, and various counters and logic control circuits. The serial-to-parallel converter is typically a serial-in, parallel-out shift register clocked by clock pulses regenerated from or synchronized with the incoming serial data stream. The parallel output of the shift register is connected to one or more sync word comparators. These are hard wired devices designed to compare the constantly changing parallel data output from the shift register with a single, predetermined unique word and to provide an output when a match occurs. To provide some flexibility, the unique word pattern can be supplied to the comparator by discrete switches, a patch panel or a latched register. The output from the comparator is used to gate the parallel output from the shift register into a buffer register and/or supply counting pulses to a counter which defines word and frame periods. The outputs from the sync word comparators are counted by counters which, by means of hard wired decoding logic, provide outputs when predetermined counts occur defining word bit length, frame word length and subframe word length.
While the prior art frame synchronizers have performed their function extremely well, their major disadvantage is that changes in data format necessitate cumbersome and expensive equipment changes.
It is therefore an object of the present invention to provide a frame synchronizer wherein data formats can be easily and dynamically changed.
It is another object of the invention to use memory array elements to provide increased flexibility in format selection and sync word selection in addition to real time reconfiguration ability in a frame synchronizer.